Modelling a $2.5 \, M_{\odot}$ Compact Star with Quark Matter

Abstract

The detection of an unexpected ∼ 2.5M component in the gravitational wave event GW190814 has puzzled the community of High-Energy astrophysicists, since in the absence of further information it is not clear whether this is the heaviest "neutron star" ever detected or either the lightest black hole known, of a kind absent in the local neighbourhood. We show in this work a few possibilities for a model of the former, in the framework of three different quark matter models with and without anisotropy in the interior pressure. As representatives of classes of "exotic" solutions, we show that even though the stellar sequences may reach this ballpark, it is difficult to fulfill simultaneously the constraint of the radius as measured by the NICER team for the pulsar PSR J0030+0451. Thus, and assuming both measurements stand, compact neutron stars can not be all made of self-bound quark matter, even within anisotropic solutions which boost the maximum mass well above the ∼ 2.5M figure. We also point out that a very massive compact star will limit the absolute maximum matter density in the present Universe to be less than 6 times the nuclear saturation value.

Maximum mass of compact stars from gravitational wave events with finite-temperature equations of state

“…In the standard interpretation [32][33][34][35][36][37][38] this is either the most massive neutron star observed to date or is a black hole that is located in the so-called mass-gap. Other, more exotic models include for example a strange star [39,40] or a compact star in an alternative theory of gravity [41]. The neutron star interpretation of the light companion in the GW190814 challenges our current understanding of the EoS, even if one assumes that this star is rotating very rapidly [32][33][34][35][36][37][38].…”

Static spherically symmetric three-form stars

“…A possibility of distinguishing quark stars in standard or CFL phase from low mass black holes or neutron stars could be through the study of thin accretion disks around rapidly rotating stars (neutron or quark), and Kerr type black holes, respectively. It was already suggested that the GW190814 event resulted from the merging of a black hole -strange quark star system [10][11][12]. Some compact astrophysical objects may contain a significant part of their matter in the form of a Bose-Einstein condensate.…”